Referring to FIG. 1, a conventional permanent, magnet rotor, as disclosed in U.S. Patent Application No. 2014015364 A1, includes a rotor yoke 1 (also known as rotor core) that is rotatable about an axis 11, and sixteen permanent magnets 2 that are disposed in the rotor yoke 1. The rotor yoke 1 is fabricated by laminating a plurality of metal plates (not shown) that have a magnetic flux density B8000 of 1.65 T or above when the magnetic field strength is 8000 A/m, and the coercivity is 100 A/m or above.
The rotor yoke 1 includes a central section 12 centered at the axis 11, a peripheral section 13 surrounding the central section 12, and a connecting section 14 connected between the central section 12 and the peripheral section 13. The peripheral section 13 includes eight outer slot units 131 equiangularly spaced apart from one another relative to the axis 11. Each of the outer slot units 131 includes two outer slots 1311 which extend along a direction parallel to the axis 11, which are spaced apart from each other and cooperatively having a generally V-shape cross section taken vertical to the axis 11, and in which two of the permanent magnets 2 are respectively received. The connecting section 14 includes eight inner slots 141 equiangularly spaced apart from one another relative to the axis 11, extending along the direction parallel to the axis 11, and arranged alternately with the outer slots units 131 in a zigzag manner relative to the axis 11.
By virtue of the configuration of the rotor yoke 1 and the material used for making the rotor yoke 1, the output torque and the efficiency of the rotor yoke 1 are improved. However, since magnetic field lines 30 of a magnetic field generated by the permanent magnets 2 tend to distribute toward the central section 12, density of the magnetic field lines 30 needs to be enhanced in order to provide a stronger magnetic field and a higher output torque.